DENVER: Barack Obama accepted the Democratic presidential nomination and pledged to help Americans recapture their country's promise after eight "failed" years of Republican policies, pushing ahead in a bid to become the US' first black president.

In a startling selection days before the start of the Republican National Convention, rival John McCain tapped little-known Alaska Governor Sarah Palin to be his vice-presidential running mate on Friday.

In an announcement, McCain's campaign said that Palin, who has been governor less than two years, "has the record of reform and bipartisanship that others can only speak of. Her experience in shaking up the status quo is exactly what is needed in Washington today".